Pyroblast is a strong fit here because Izzet Delver is built almost entirely out of blue cards. Daze, Force of Will, Flow State, Brainstorm, Ponder and Spell Pierce are all legal targets for the counter mode, and the destroy mode answers a Murktide Regent outright regardless of how many counters it entered with. Abrade can kill a Dragon's Rage Channeler or a Murktide Regent that hasn't grown past 3 toughness for 3 damage, or destroy Cori-Steel Cutter to deny their equipment plan. Omniscience is far too slow against this fast aggressive clock backed by Lightning Bolt and Wasteland, so it comes out. Flusterstorm comes out too: against a deck full of cheap spells and Daze, the opponent can often pay the tax, so it has fewer high-value targets.